116 THE DIRECT INFLUENCE 



tageous rate with relation to each other within, 

 for example, some narrow range of temperature. 

 In our easy acceptance of the obvious, we are apt 

 to assume that these optimal conditions are fur- 

 nished by the native habitats of plants, or in other 

 words, the place they happen to occupy in their 

 movements about the world when they are called 

 to our attention. Now, on the one hand, plants 

 simply are found in areas they have been able to 

 reach, and " native habitats " may by no means 

 offer the optimal conditions, a condition of affairs 

 of which more than a hint is furnished by the 

 irruption of weeds, followed by a development 

 of a vigor unknown within the previous range of 

 the species. On the other, the reminder is neces- 

 sary that no one habitat may furnish the optima 

 for the accomplishment of all of the processes 

 involved in the ontogeny and reproduction of the 

 individual, and all environic relations include 

 groups of compromises and of adjustments that 

 put the capacity of the living matter to the ut- 

 most stresses it may bear. 



Two main considerations arise when attention 

 is directed to the behavior of the organism as it 

 encounters the external factors in unusual inten- 

 sities, an experience which has been countlessly 

 repeated and which is one of the eliminating fac- 

 tors in selection. The first concerns the mechan- 

 ism of the adjustment of the individual to alter- 

 ing environment, and the second, the possibilities 

 of transmission of the effects of the adjustment 



